<sub>Well, since the question was updated (and other issues aroused), I updated my answer.</sub>

First of all, I am not sure whether using Russian language in questions and answers at all is allowed by [higher-level Stack Exchange rules/policies](http://discuss.area51.stackexchange.com/q/20988/146894) (you should understand, that not the whole Stack Exchange is community-driven; hosted sites are, but top-management also exists). If it is, then this discussion makes sense. If it isn't, then current discussion makes sense only in the context like: "Should we allow Russian language with our local rules/norms, if higher-level Stack Exchange rules/policies would allow it someday?"

Second, my original thoughts were not about trilingual site, but rather about [allowing every language](http://discuss.area51.stackexchange.com/a/22567/146894) (I had written that draft for local rules/norms *before* I realized I am not sure it's allowed by higher-level rules/policies). My idea was something like "Ukrainian is strongly preferred; you *are allowed* to ask in *any* language — with some languages the probability to get answer is drastically lower — still you may try"). If we're talking about giving Russian some special status among other languages, I'd rather say "no".

Sorry for those who have up-voted my answer (before I changed it). You're free to revoke your votes (or even vote it down).

<sub>My original answer goes below:</sub>
> <sub>That's my opinion:<br>
> http://discuss.area51.stackexchange.com/a/22567/146894</sub>
> 
> <sub>TL;DR: I don't see how we can forbid other languages (and Russian, despite all political issues, is one of them). However, I think users should endeavor to write in Ukrainian. Maybe, political preferences will come out anyway (e.g. when seeing question in Russian, some users will expressly answer in Ukrainian, even having advanced level of Russian and theoretically not knowing a level of questioner's ability to understand Ukrainian), but we should not encourage that.</sub>